1. Field
The present disclosure relates to an omnidirectional light emitting device lamp, and more particularly, to an omnidirectional light emitting device lamp having a light distribution characteristic having a large range similar to that of a general incandescent lamp.
2. Description of the Related Art
Light emitting diodes (LEDs) are, for example, semiconductor light emitting devices that convert an electric signal to light using the properties of a compound semiconductor. A semiconductor light emitting device such as an LED, compared to other existing light emitting bodies, has characteristically a long life span and uses a low voltage and simultaneously has low power consumption. Also, a semiconductor light emitting device has merits, for example, a fast response speed and superior shock-resistance, and may be manufactured to be small and light. When necessary, a semiconductor light emitting device is capable of generating light of different wavelengths according to the type and composition of a semiconductor in use. Also, it is a recent trend to replace an existing fluorescent lamp or incandescent lamp with an illumination apparatus using a high brightness light emitting device chip.
For example, an LED bulb may mainly include a base, a heat radiating structure, a driving circuit, a printed circuit board (PCB), an LED, and a cover. The cover is formed of glass having a hemispherical shape, or plastic such as acryl or polycarbonate. Also, to prevent the LED in the bulb from being directly seen, with respect to a glass cover, a white diffusion coating is formed on an inner surface of the glass cover, whereas with a plastic cover, the plastic cover is manufactured of a cover member with a diffusion agent mixed therein to realize a light diffusion effect.
However, an illumination lamp using a semiconductor light emitting device emits light only in a front direction, not in all radial directions in 360 degrees, and thus the light distribution characteristic of the illumination lamp using a semiconductor light emitting device is quite different from that of an incandescent lamp. For example, the above-described LED bulb emits the most amount of light in a forward direction at zero degrees. At greater degrees, the amount of light emission decreases, and the amount of light emission is almost zero at about ±90 degrees. In contrast, in a general incandescent lamp, the amount of light emission hardly decreases and is maintained constant from about zero degrees to about ±130 degrees. Accordingly, while the full width at half maximum of an irradiation angle of the LED bulb is about 130 degrees, the full width at half maximum of a general incandescent lamp is about 260 degrees, which is quite different from that of the LED bulb. The difference is generated because, while a filament used for a general incandescent lamp emits light in all directions in 360 degrees, the LED bulb emits light in the forward direction in about 120 degrees only. Thus, when the LED bulb is used in an existing illumination apparatus, the LED bulb provides users with a distribution of light or a sense of illumination that is quite different from that with which users are familiar. This may be a hindrance to distribution of LED bulbs.